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84                               CHEMICAL ENGINEERING
TABLET 5.—HOISTING SPEEDS OF STANDARD OVERHEAD ELECTRIC CRANES
	Speeds in feet per minute								
Rated	Class								
capacity									
in tons	Low			Medium			High		
	First	Second	Third	First	Second	Third	First	Second	Third
5	27	34	40	47	60	70	66	83	100
10	20	24	30	37	48	57	50	62	75
15	16	20	24	29	36	42	40	50	60
20	14	17	20	24	28	34	32	40	48
25	12	15	18	20	24	28	28	34	40
30	11	14	16	18	21	24	24	29	35
40	9	11	14	16	18	21	21	25	30
50	8	10	12	14	16	19	19	22	26
60	7	9	11	13	15	18	18	20	24
75	6	8	10	12	14	17	17	19	22
100	5	6	9	10	12	15	15	17	20
150	4	5	7	8	10	12	12	15	18
Where,       Q = rated capacity of crane in tons,
HS = minimum, or first, hoisting speed in feet per minute, TS = trolley speed in feet per minute, BS = bridge speed in feet per minute, and L = span of bridge in feet.
TABLE 6.—COMPARATIVE COSTS OF STANDARD OVERHEAD ELECTRIC CRANES
Span in feet
Rated capacity								100
	20	25	30	35	40	50	75	
5	0.80	1.00	1.03	1.07	1.10	1.20	1.40	1.70
10	1.20	1.25	1.30	1.35	1.40	1.50	1.80	2.15
15	1.40	1.45	1.51	1.57	1.62	1.75	2.09	2.54
20	1.59	1.64	1.70	1.77	1.83	1.98	2.35	2.88
25	1.65	1.80	1.88	1.94	2.01	2.17	2.61	3.19
30	1.90	1.97	2.04	2.10	2.19	2.38	2.88	3.50
50		2.50	2.60	2.70	2.80	3.00	3.52	4.18
75		3.10	3.20	3.35	3.41	3.68	4.32	5.18
100		3.60	3.71	3.85	3.99	4.25	5.00	
150		4.28	4.40	4.52	4.67	4.98		
Cost.—The cost of overhead electric cranes varies between quite wide limits, but reliable approximations can be arrived at by comparative costs based on a known cost of some specific crane of standard type and given span. Index values based on